Traction is frequently prescribed to treat people suffering from pain in the back, neck or other parts of the body. This pain is often caused by abnormalities of the spinal column, such as misalignment of the vertebrae, slipping or rupture or erosion of the discs betwen the vertebrae, etc., all causing pinching or impingement on the nerves running through the vertebrae and resulting in intense and continuous pain. The proper application of tractive force on the spinal column whereby the vertebrae are eased apart slightly is known to relieve this pressure on the nerves thereby reducing the pain and, in some instances, aiding in curing the underlying cause of the pain.
Various mechanical and electrical devices have been used to apply tractive force to the spinal column of patients in sitting, standing or reclining positions. One way of applying such tractive force to a patient is to tether him at one end or the other of his body, depending on where in his spinal column it is desired to apply the traction, and allowing the weight of his body, through gravity, to provide the tractive force. For example, if it is desired to apply traction to the cervical (neck) vertebrae, the patient is tethered by the chin and suspended therefrom, whereas, if it is desired to apply traction to the lumbar (lower back) vertebrae, he is tethered by the ankles and suspended upside down.
Maximum gravitational tractive force is obtained by suspending the patient in a vertical position. However, not only do most people find the upside-down position (when suspended by the ankles) disorienting and unsettling but, also, the application of 100% of a patient's body weight as a tractive force on his spinal column can be excessive and itself cause pain and even harm. It is necessary, therefore, to find a way of reducing the gravitational tractive force on the patient. This can be done by supporting the patient on an inclinable plane surface while suspending him from one end or the other of his body. The amount of gravitational force can then be adjusted by varying the angle of inclination of the supporting surface. When the inclinable surface is horizontal, the gravitational tractive force is 0% of body weight; i.e., there is no traction. When the inclinable surface is vertical, the gravitational tractive force is 100% of the patient's body weight.
Another force that has to be taken into account when applying gravitational traction in the way outlined above is the friction between the patient and the inclinable surface on which he is lying. At low angles of inclination, this frictional force is greater than the gravitational force so that the patient does not slide down the inclined surface and, therefore, no traction is exerted on his spinal column. It is not until the gravitational force, increased by increasing the angle of inclination of the supporting surface, is greater than the frictional force holding the patient to that surface that the patient can slide down the inclined surface away from the tether to which he is attached and, thus, get the benefit of his body weight as a tractive force on his spinal column. However, it is essential that, when the gravitational force overcomes the frictional force, it does not do so suddenly or else the patient will be subjected to an abrupt and possibly painful or harmful jerk.
A device that applies gravitational principles is illustrated in U.S. Pat. No. 4,205,665 to Burton. This device comprises an adjustable inclined hospital bed, rotating hoops, and a traction bar. A chest harness is wrapped around the patient's thorax and connected to the traction bar by straps and a tethering cable. The patient is thereby suspended by the rib cage from above his shoulders. The force of gravity on the lower body provides the tractive force on the lower back. This combination of a hospital bed and an elaborate framework is appropriate for use in a hospital, but it is not ideal for use in the home. Moreover, as explained above, the friction caused by contact of the patient with the bed tends to counteract the gravitational pull, particularly at low angles of inclination. As the bed is raised towards the vertical the overcoming of this friction can cause uncomfortable jarring to the patient.